IFT 372 WIRELESS COMMUNICATION -
HELM - QUIZ 1-7 + MIDTERM +
LECTURE ACTIVITIES. EXAM
QUESTIONS AND ANSWERS 100% PASS
What is a logarithm? - ANS A logarithm is an exponent based mathematical representation of
a numerical value.
What logarithmic base is used in digital communications? - ANS Two
How do you find a log2 value on a calculator that only has log10 functionality? (Hint: what is the
formula?) - ANS log2(a) = [log10(a) / log10(2)]
What is the definition of a decibel? - ANS A decibel is a mathematical representation of a
power level on a logarithmic scale.
a = 10lob(b), where a is the decibel value and b is the decimal value.
You cannot mix decimal and decibel values in an equation (i.e., you either have to work with
decimal values or decibel values) - ANS True
There can be more than one power value in a decibel (dB) equation. - ANS False
1 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
,When you add two decibel values, you are multiplying those values in decimal (I.e. 3 dB + 6 dB =
9 dB which is equivalent to 2 * 4 = 8 in decimal) - ANS True
__________ is a decibel value referenced to watts and ______ is a decibel value referenced to
milliwatts. - ANS dBW & dBm
How do you convert dBW to dBm? - ANS Add 30 dB to dBW to obtain dBm value
The net gain or (loss) of a transmission system is a radio between the _________ __________
and ____________ ____________ where the ___________ is the numerator and the
___________ ____________ is the denominator. - ANS Output power & Input power
What parameter of the intelligent signal causes or determines the instantaneous rate of carrier
frequency? - ANS Amplitude of the modulating signal
What parameter of the intelligent signal causes frequency deviation of the carrier? -
ANS Amplitude of the modulating signal
A modulated carrier occupies a single frequency. - ANS False
Determine the noise power (in dBm) at 27° C in a 500 kHz bandwidth. - ANS PN = 10 log
(1.38*10^-23*(27+273)*500kHz)
= -146.8 dBw
=> -116.8 dBm
Determine the noise power (in dBm) at 27° C in a 20 MHz bandwidth system. - ANS Pn=kTB;
k=1.38*(10^-23)W°K-Hz; T(°K)=27°C+273=300°K;
2 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
,B=20*10^6Hz
=10log(1.38*(10^-23)*300*20*10^6)
=10log(8.28*(10^-14))
=-130.82 dBW
=-130.82 dBW +30 dB
=-100.8 dBm
Determine the noise power (in dBm) at 23°C in a 500 kHz bandwidth. - ANS k = 1.38 * 10^23
T = 27 + 273 = 300
B = 5e5
PN = 10log(kTB)
= 10log(1.38 * 10^23 * 300 * 5e5)
= -146.8
= -146.8 + 30 dB
= -116.8 dBm
For a 12-bit linear sign-magnitude PCM code with a resolution of 0.02 V, determine the voltage
range that would be converted to the PCM code 110000000000 - ANS 1024 * .02 => 20.47V
to 20.49V
An FM signal has a deviation of 75 kHz and a modulating frequency of 15 kHz. The carrier
frequency is 1600 MHz. Using Carson's rule, what is the required bandwidth for this system? -
ANS BSCR = 2 * (75kHz + 15kHz) = 180kHz
Which of the following are strengths of OFDM? - ANS Frequency selective fading does not
adversely affect all subcarriers & effectively uses the wireless spectrum.
3 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
, Given a three stage amplifier system with stage 1 having a gain of 16 dB and a NF=3.5 dB, Stage
2 gain of 19 dB and a NF = 4.8 dB, Stage 3 having a gain of 20 dB and a NF = 6.2 dB, calculate the
system noise figure. - ANS 16 dB => 40;
3.5 dB => 2.24;
19 dB => 80;
4.8 dB => 3.02;
20 dB => 100;
6.2 dB => 4.17
F = 2.24 + ((3.02-1)/40) + ((4.17-1)/(40*80))
= 2.29 => 3.6 dB
Consider an OFDM implementation that uses 15 kHz subcarriers and use an OFDM symbol of
2048 subcarriers. The nominal cyclic prefix accounts for a 7% guard time. The extended cyclic
prefix can use up to 25%. 1600 subcarriers can be used for data transmission. The rest are
needed for pilot and null subcarriers. The transmission bandwidth is 25 MHz using 8 QAM
modulation.
What is the data rate for the nominal CP? - ANS R = 25MHz * (1600 / [2048 + 205])*5=88.8
Mbps
What is the effective Temperature (Te in °K) for a system with a 29 dB input SNR and a 23 dB
output SNR? - ANS Noise Factor (F) = 10^2.^2.3 => 4
Effective Temp (Te) = (F - 1) * 290
= (4 - 1) * 290
= 3 * 290
= 870
OR
F = (1 + Te/290)
4 = (1 + Te/290)
4 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
HELM - QUIZ 1-7 + MIDTERM +
LECTURE ACTIVITIES. EXAM
QUESTIONS AND ANSWERS 100% PASS
What is a logarithm? - ANS A logarithm is an exponent based mathematical representation of
a numerical value.
What logarithmic base is used in digital communications? - ANS Two
How do you find a log2 value on a calculator that only has log10 functionality? (Hint: what is the
formula?) - ANS log2(a) = [log10(a) / log10(2)]
What is the definition of a decibel? - ANS A decibel is a mathematical representation of a
power level on a logarithmic scale.
a = 10lob(b), where a is the decibel value and b is the decimal value.
You cannot mix decimal and decibel values in an equation (i.e., you either have to work with
decimal values or decibel values) - ANS True
There can be more than one power value in a decibel (dB) equation. - ANS False
1 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
,When you add two decibel values, you are multiplying those values in decimal (I.e. 3 dB + 6 dB =
9 dB which is equivalent to 2 * 4 = 8 in decimal) - ANS True
__________ is a decibel value referenced to watts and ______ is a decibel value referenced to
milliwatts. - ANS dBW & dBm
How do you convert dBW to dBm? - ANS Add 30 dB to dBW to obtain dBm value
The net gain or (loss) of a transmission system is a radio between the _________ __________
and ____________ ____________ where the ___________ is the numerator and the
___________ ____________ is the denominator. - ANS Output power & Input power
What parameter of the intelligent signal causes or determines the instantaneous rate of carrier
frequency? - ANS Amplitude of the modulating signal
What parameter of the intelligent signal causes frequency deviation of the carrier? -
ANS Amplitude of the modulating signal
A modulated carrier occupies a single frequency. - ANS False
Determine the noise power (in dBm) at 27° C in a 500 kHz bandwidth. - ANS PN = 10 log
(1.38*10^-23*(27+273)*500kHz)
= -146.8 dBw
=> -116.8 dBm
Determine the noise power (in dBm) at 27° C in a 20 MHz bandwidth system. - ANS Pn=kTB;
k=1.38*(10^-23)W°K-Hz; T(°K)=27°C+273=300°K;
2 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
,B=20*10^6Hz
=10log(1.38*(10^-23)*300*20*10^6)
=10log(8.28*(10^-14))
=-130.82 dBW
=-130.82 dBW +30 dB
=-100.8 dBm
Determine the noise power (in dBm) at 23°C in a 500 kHz bandwidth. - ANS k = 1.38 * 10^23
T = 27 + 273 = 300
B = 5e5
PN = 10log(kTB)
= 10log(1.38 * 10^23 * 300 * 5e5)
= -146.8
= -146.8 + 30 dB
= -116.8 dBm
For a 12-bit linear sign-magnitude PCM code with a resolution of 0.02 V, determine the voltage
range that would be converted to the PCM code 110000000000 - ANS 1024 * .02 => 20.47V
to 20.49V
An FM signal has a deviation of 75 kHz and a modulating frequency of 15 kHz. The carrier
frequency is 1600 MHz. Using Carson's rule, what is the required bandwidth for this system? -
ANS BSCR = 2 * (75kHz + 15kHz) = 180kHz
Which of the following are strengths of OFDM? - ANS Frequency selective fading does not
adversely affect all subcarriers & effectively uses the wireless spectrum.
3 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
, Given a three stage amplifier system with stage 1 having a gain of 16 dB and a NF=3.5 dB, Stage
2 gain of 19 dB and a NF = 4.8 dB, Stage 3 having a gain of 20 dB and a NF = 6.2 dB, calculate the
system noise figure. - ANS 16 dB => 40;
3.5 dB => 2.24;
19 dB => 80;
4.8 dB => 3.02;
20 dB => 100;
6.2 dB => 4.17
F = 2.24 + ((3.02-1)/40) + ((4.17-1)/(40*80))
= 2.29 => 3.6 dB
Consider an OFDM implementation that uses 15 kHz subcarriers and use an OFDM symbol of
2048 subcarriers. The nominal cyclic prefix accounts for a 7% guard time. The extended cyclic
prefix can use up to 25%. 1600 subcarriers can be used for data transmission. The rest are
needed for pilot and null subcarriers. The transmission bandwidth is 25 MHz using 8 QAM
modulation.
What is the data rate for the nominal CP? - ANS R = 25MHz * (1600 / [2048 + 205])*5=88.8
Mbps
What is the effective Temperature (Te in °K) for a system with a 29 dB input SNR and a 23 dB
output SNR? - ANS Noise Factor (F) = 10^2.^2.3 => 4
Effective Temp (Te) = (F - 1) * 290
= (4 - 1) * 290
= 3 * 290
= 870
OR
F = (1 + Te/290)
4 = (1 + Te/290)
4 @COPYRIGHT 2025/2026 ALLRIGHTS RESERVED.
